Protein is an essential nutritional factor for a.o. mammals and layers. Most livestock and many human beings get the necessary proteins from vegetable protein sources. Important vegetable protein sources are e.g. cereals, legumes and oilseed crops.
Hydrolyzed vegetable proteins, such as soy protein hydrolysates, find application as nutrients, e.g. as nutritional additives to foods and beverages. Hydrolyzed proteins are absorbed more easily than unhydrolysed protein, whey protein hydrolysates are considered having the highest nutritional value. Several methods for preparing protein hydrolysates are known and described in the literature, cf. e.g. U.S. Pat. No. 4,324,805 and WO 92/15696.
Essentially all food and feed substances originating from plants contain phytate and phytic acid as a storage phosphorus source [cf. review in E. Graf (ed.), Phytic Acid, Chemistry and Applications, Minneapolis, U.S.A., 1986]. About 75-78% of the phosphorus in cereals is bound as phytic acid. Phytate comprises 1-3% of all nuts, cereals, legumes, oil seeds, spores and pollen. Complex salts of phytic acid are termed phytin.
Phytic acid chelates minerals such as calcium, zinc, magnesium, and iron, thereby decreasing the bio-availability of nutritionally important minerals, and is generally considered an anti-nutritional factor. In vitro studies indicate that phytic acid inhibits the peptic digestion of some animal proteins, whereas the trypsin digestion was unaffected [cf. Knuckles et al., Journal of Food Science. 1989 54 1348-1350].
Phytases are enzymes which catalyze the conversion of phytate to inositol and inorganic phosphorus. Phytases have been obtained from e.g. Bacillus, Pseudomonas, Saccharomyces and Aspergillus.
In U.S. Pat. No. 3,297,548 it has been suggested to add microbial phytase to feedstuffs of monogastric animals in order to avoid supplementing the feed with inorganic phosphorus.
It has also been conceived that phytases may be used in the processing of soy. Thus EP-A-0 420 358 reports that soybean meal contains high levels of the anti-nutritional factor phytate which renders this protein source unsuitable for application in baby food, as well as in feed for fish, calves and other non-ruminants, since the phytate chelates essential minerals present therein.
In summary it has previously been suggested to use phytase enzymes either for exploiting the phosphorus bound in the phytate/phytic acid present in vegetable protein sources, or for exploiting the nutritionally important minerals bound in phytic acid complexes.
However, there is a need for improving the availability of the proteins present in vegetable sources, e.g. cereals, legumes and oilseed crops, since an increased availability leads to higher yields of protein hydrolyzing processes as well as nutritional benefits, i.e. improved protein utilization.